1. Field of the Invention
The present invention relates to a liquid ejecting apparatus to be used in, for example, an ink jet recording head of an ink jet printer for recording an image by shooting ink droplets and, in particular, to a liquid ejecting apparatus which is of high accuracy and which is capable of forming a high quality image through high accuracy shooting of ink droplets and achieving an improvement in terms of yield. The present invention also relates to an ink jet printer using such a liquid ejecting apparatus.
2. Description of the Related Art
A thermal ink jet, which rapidly vaporizes a portion of ink through heating by a heater and causes ink droplets to be ejected through nozzles (orifices) by its expansion force or the like, is utilized in various types of printers (See JP 48-9622 A, JP 54-51837 A, etc.).
Apart from this, a printer is known which utilizes an electrostatic ink jet in which an oscillation plate is caused to oscillate by an MEM (micro electronic machine) utilizing static electricity, ejecting ink droplets through nozzles by the energy thereof (See JP 11-309850 A, etc.).
Of those, FIGS. 7A and 7B schematically show an example of a thermal ink jet recording head. FIG. 7A is a plan view of an ink jet recording head as seen from the ink ejecting direction, and FIG. 7B is a sectional view taken along the line IVxe2x80x94IV of FIG. 7A.
As shown in FIG. 7A, in a recording head 150, a large number of nozzles 20 for ejecting ink are arranged in one direction (in FIG. 7B, in a direction perpendicular to the plane of the drawing). In the example shown, the nozzles 20 are arranged in two rows (hereinafter referred to as nozzle rows), thereby increasing the nozzle density.
In this recording head 150, there are directly formed on the surface of a semiconductor substrate such as an Si (silicon) substrate 152 heaters (not shown) corresponding to the individual nozzles 20 and serving as ink ejecting devices, a driving LSI 14 for driving each heater, a partition 15 forming ink flow passages to the nozzles 20, etc. The nozzles (orifices) 20 are formed in an orifice plate 22 laminated/glued to the Si substrate 152 (partition 15).
Further, formed in the silicon substrate 152 of the recording head 150 are an ink groove 16 for supplying ink to the ink flow passages and ink supply holes 18 for supplying ink to the ink groove 16. The ink groove 16 is formed by digging the surface of the silicon substrate 152 and extends in the nozzle row direction. The ink supply holes 18, which make the back side of the Si substrate 152 communicate with the ink groove 16, are formed and arranged at predetermined intervals in the nozzle row direction.
In the recording head 150, ink is supplied to the ink supply holes 18 from the back side of the Si substrate 152 and introduced into the ink groove 16 communicating therewith. From the ink groove 16, the ink flows through the ink passages formed by the partition 15 and leading to the nozzles 20 before it is ejected through the nozzles 20 by being heated by the heaters.
Usually, this recording head 150 is not handled in the form of an Si chip (semiconductor chip) based on the Si substrate 152; it is glued (mounted) to a frame 24 and attached, for example, to a head unit (e.g., a so-called cartridge) of an ink jet printer.
Further, formed in the frame 24 is an ink flow passage 26 for supplying ink from an ink tank of the head unit to the ink supply holes 18 of the recording head 150.
In the recording head 150 (including not only the thermal ink jet shown but also the above-mentioned electrostatic type), in which ink ejecting devices such as heaters are formed in the Si substrate 152, one of the factors leading to a deterioration in product accuracy and yield is warpage (curving) of the recording head 150 (Si substrate 152).
Such warpage naturally leads to positional error of the nozzles 20, i.e., a deterioration in image quality. In extreme cases, the product becomes defective (NG). When the recording head 150 is elongated, this warpage is aggravated and the relative mechanical strength of the head deteriorates, with the result that the above problem becomes more serious.
Various attempts have been made to overcome the problem of such warpage. For example, provision of a reinforcing layer (counter layer) on the back side of the Si substrate 152 and reconsideration of the material of the orifice plate 22 have been proposed. However, no sufficient effect has been achieved yet.
It might be possible to eliminate such warpage of the recording head 150 by mounting to the frame 24 the recording head 150 in a straight state by using a strong adhesive. However, that would make it necessary to keep the recording head 150 in a pressed state until the adhesive cures completely, which is very disadvantageous in terms of productivity and operability. Further, it would be very difficult to straighten the recording head 150 in a stable manner. Moreover, such a method involves application of an excessive force to the recording head 150, so that, in many cases, the method will lead to breakage of the recording head 150 instead of straightening it.
According to this method however, even if the recording head 150 can be straightened well, when the strength is reduced due to secular changes, the recording head 150 may be warped again or be broken because of the residual stress being applied, whereupon the service life of the recording head 150 may be shortened.
The present invention has been made with a view toward solving the above problem in the prior art. It is an object of the present invention to provide a liquid ejecting apparatus for use in an ink jet recording head or the like in which liquid ejecting devices such as heaters and MEMs are formed on an Si (silicon) substrate prepared by using, for example, a semiconductor manufacturing technique, in which little warpage is involved, which has a long service life and wherein it is possible to obtain a high accuracy product with high yield even in the case where the apparatus has a line structure with a long nozzle row.
Another object of the present invention is to provide an ink jet printer using the liquid ejecting apparatus as an ink jet recording head.
In order to attain the object described above, the first aspect of the present invention provides a liquid ejecting apparatus comprising: a plurality of liquid ejecting devices which are arranged in one direction on a silicon substrate; and a plurality of liquid ejecting nozzles which are arranged in correspondence with the plurality of liquid ejecting devices, wherein at least part of the silicon substrate has a thickness of not less than 700 xcexcm.
Preferably, the at least part of the silicon substrate which has the thickness of not less than 700 xcexcm is positioned along the one direction in which the plurality of liquid ejecting devices are arranged.
Preferably, the silicon substrate has a portion of which the thickness is continuously not less than 700 xcexcm from end to end in the one direction in which the plurality of liquid ejecting devices are arranged.
Preferably, the plurality of liquid ejecting devices form a length of not less than 10 mm in the one direction in which the plurality of liquid ejecting devices are arranged.
Preferably, a liquid is ejected in a direction substantially perpendicular to a surface of the silicon substrate.
Preferably, the liquid ejecting apparatus is an ink jet recording head.
Preferably, the silicon substrate has a length of not less than 10 mm in the one direction in which the plurality of liquid ejecting devices are arranged.
Preferably, the plurality of liquid ejecting nozzles have a nozzle density of 600 nozzles/inch or more.
Preferably, the silicon substrate has an aspect ratio of 2 to 20 in terms of a ratio of length to width.
In order to attain the object described above, the second aspect of the present invention provides an ink jet printer comprising: an ink jet recording head which includes: a plurality of ink ejecting devices arranged in one direction on a silicon substrate; and a plurality of ink ejecting nozzles arranged in correspondence with the plurality of ink ejecting devices, wherein at least part of the silicon substrate has a thickness of not less than 700 xcexcm.
Preferably, the at least part of the silicon substrate which has the thickness of not less than 700 xcexcm is positioned along the one direction in which the plurality of ink ejecting devices are arranged.
Preferably, the silicon substrate has a portion of which the thickness is continuously not less than 700 xcexcm from end to end in the one direction in which the plurality of ink ejecting devices are arranged.
Preferably, the plurality of ink ejecting devices form a length of not less than 10 mm in the one direction in which the plurality of ink ejecting devices are arranged.
Preferably, ink is ejected in a direction substantially perpendicular to a surface of the silicon substrate.